The present invention relates generally to electronic circuit characterization and simulation techniques. More particularly, embodiments provide methods, systems, and computer-readable storage mediums for determining phase-noise characteristics for circuits having an oscillator.
Accurate oscillator phase-noise characterization may be critical in the design of some RF and microwave communication systems. As IC voltage references, such as bandgap references for example, are widely used as DC biasing circuitry in deep-submicron low noise RF oscillator design because of its insensitivity to temperature and load variations, the phase noise at low offset frequency can be dominated by the thermal and flicker noises generated by the voltage reference.
Some methods of phase noise analysis may involve time-domain methods, such as shooting Newton method. Merely by way of example, a procedure of the shooting Pnoise analysis may involve the following: 1) Assemble a matrix to compute a transfer function; 2) because the matrix equation may be close to singular for small offset-frequency, the dominant mode (whose eigen-value is zero) may be extracted; 3) separate the solution to the matrix equation into two parts—the part in parallel with the dominant mode and the part vertical to the dominant mode; and solve them separately; and 4) combine the two parts together into the solution to the matrix equation.
This shooting-Pnoise method may work well for some circuits. However, there may exist an increasingly large number of oscillators on which the shooting-Pnoise may fail or give wrong phase-noise results. There may be different categories of the problems. For example, the shooting-Pnoise may fail to extract a unique dominant mode. Even if the dominant mode is extracted, the calculated phase-noise may fail to include the noise contribution from a voltage supply, for example. The low-frequency noise from voltage supply may be up-converted to the first harmonics and may show a hump at small offset frequency. However, the shooting-Pnoise may not capture this behavior.
The cause of both problems may be because the algorithm of the shooting-Pnoise is not valid for some oscillators, for example, oscillators with voltage supply of large time-constant. The assumption that the solution can be separated completely using a frequency-independent eigen-mode may be wrong in these cases.
There is thus a need for tools and techniques that provide a robust and accurate approach to simulate the phase-noise, especially to compute noise contribution due to the voltage supply with large time-constant.